1. Technical Field
The present disclosure relates to methods for reporting channel state information, CSI, from a mobile station to a base station in a mobile communication system, particularly on unlicensed carriers. The present disclosure is also providing mobile stations for performing the methods described herein.
2. Description of the Related Art
Long Term Evolution (LTE)
Third-generation mobile systems (3G) based on WCDMA radio-access technology are being deployed on a broad scale all around the world. A first step in enhancing or evolving this technology entails introducing High-Speed Downlink Packet Access (HSDPA) and an enhanced uplink, also referred to as High Speed Uplink Packet Access (HSUPA), giving a radio access technology that is highly competitive.
In order to be prepared for further increasing user demands and to be competitive against new radio access technologies, 3GPP introduced a new mobile communication system which is called Long Term Evolution (LTE). LTE is designed to meet the carrier needs for high speed data and media transport as well as high capacity voice support for the next decade. The ability to provide high bit rates is a key measure for LTE.
The work item (WI) specification on Long-Term Evolution (LTE) called Evolved UMTS Terrestrial Radio Access (UTRA) and UMTS Terrestrial Radio Access Network (UTRAN) is finalized as Release 8 (LTE Rel. 8). The LTE system represents efficient packet-based radio access and radio access networks that provide full IP-based functionalities with low latency and low cost. In LTE, scalable multiple transmission bandwidths are specified such as 1.4, 3.0, 5.0, 10.0, 15.0, and 20.0 MHz, in order to achieve flexible system deployment using a given spectrum. In the downlink, Orthogonal Frequency Division Multiplexing (OFDM) based radio access was adopted because of its inherent immunity to multipath interference (MPI) due to a low symbol rate, the use of a cyclic prefix (CP) and its affinity to different transmission bandwidth arrangements. Single-carrier frequency division multiple access (SC-FDMA) based radio access was adopted in the uplink, since provisioning of wide area coverage was prioritized over improvement in the peak data rate considering the restricted transmit power of the user equipment (UE). Many key packet radio access techniques are employed including multiple-input multiple-output (MIMO) channel transmission techniques and a highly efficient control signaling structure is achieved in LTE Rel. 8/9.
LTE Architecture
The overall architecture is shown in FIG. 1 and a more detailed representation of the E-UTRAN architecture is given in FIG. 2. The E-UTRAN consists of an eNodeB, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the user equipment (UE). The eNodeB (eNB) hosts the Physical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data Control Protocol (PDCP) layers that include the functionality of user-plane header-compression and encryption. It also offers Radio Resource Control (RRC) functionality corresponding to the control plane. It performs many functions including radio resource management, admission control, scheduling, enforcement of negotiated uplink Quality of Service (QoS), cell information broadcast, ciphering/deciphering of user and control plane data, and compression/decompression of downlink/uplink user plane packet headers. The eNodeBs are interconnected with each other by means of the X2 interface.
The eNodeBs are also connected by means of the S1 interface to the EPC (Evolved Packet Core), more specifically to the MME (Mobility Management Entity) by means of the S1-MME and to the Serving Gateway (SGVV) by means of the S1-U. The S1 interface supports a many-to-many relation between MMEs/Serving Gateways and eNodeBs. The SGW routes and forwards user data packets, while also acting as the mobility anchor for the user plane during inter-eNodeB handovers and as the anchor for mobility between LTE and other 3GPP technologies (terminating S4 interface and relaying the traffic between 2G/3G systems and PDN GW). For idle state user equipments, the SGW terminates the downlink data path and triggers paging when downlink data arrives for the user equipment. It manages and stores user equipment contexts, e.g., parameters of the IP bearer service, network internal routing information. It also performs replication of the user traffic in case of lawful interception.
The MME is the key control-node for the LTE access-network. It is responsible for idle mode user equipment tracking and paging procedure including retransmissions. It is involved in the bearer activation/deactivation process and is also responsible for choosing the SGW for a user equipment at the initial attach and at time of intra-LTE handover involving Core Network (CN) node relocation. It is responsible for authenticating the user (by interacting with the HSS). The Non-Access Stratum (NAS) signaling terminates at the MME and it is also responsible for generation and allocation of temporary identities to user equipments. It checks the authorization of the user equipment to camp on the service provider's Public Land Mobile Network (PLMN) and enforces user equipment roaming restrictions. The MME is the termination point in the network for ciphering/integrity protection for NAS signaling and handles the security key management. Lawful interception of signaling is also supported by the MME. The MME also provides the control plane function for mobility between LTE and 2G/3G access networks with the S3 interface terminating at the MME from the SGSN. The MME also terminates the S6a interface towards the home HSS for roaming user equipments.
Component Carrier Structure in LTE
The downlink component carrier of a 3GPP LTE system is subdivided in the time-frequency domain in so-called subframes. In 3GPP LTE each subframe is divided into two downlink slots as shown in FIG. 3, wherein the first downlink slot comprises the control channel region (PDCCH region) within the first OFDM symbols. Each subframe consists of a given number of OFDM symbols in the time domain (12 or 14 OFDM symbols in 3GPP LTE (Release 8)), wherein each OFDM symbol spans over the entire bandwidth of the component carrier. The OFDM symbols thus each consist of a number of modulation symbols transmitted on respective NDLRB*NRBsc subcarriers as also shown in FIG. 4.
Assuming a multi-carrier communication system, e.g., employing OFDM, as, for example, used in 3GPP Long Term Evolution (LTE), the smallest unit of resources that can be assigned by the scheduler is one “resource block”. A physical resource block (PRB) is defined as NDLsymb consecutive OFDM symbols in the time domain (e.g., 7 OFDM symbols) and NRBsc consecutive subcarriers in the frequency domain as exemplified in FIG. 4 (e.g., 12 subcarriers for a component carrier). In 3GPP LTE (Release 8), a physical resource block thus consists of NDLsymb*NRBsc resource elements, corresponding to one slot in the time domain and 180 kHz in the frequency domain (for further details on the downlink resource grid, see, for example, 3GPP TS 36.211, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)”, section 6.2, available at http://www.3gpp.org and incorporated herein by reference).
One subframe consists of two slots, so that there are 14 OFDM symbols in a subframe when a so-called “normal” CP (cyclic prefix) is used, and 12 OFDM symbols in a subframe when a so-called “extended” CP is used. For sake of terminology, in the following the time-frequency resources equivalent to the same NRBsc consecutive subcarriers spanning a full subframe are called a “resource block pair”, or equivalent “RB pair” or “PRB pair”.
The term “component carrier” refers to a combination of several resource blocks in the frequency domain. In future releases of LTE, the term “component carrier” is no longer used; instead, the terminology is changed to “cell”, which refers to a combination of downlink and optionally uplink resources. The linking between the carrier frequency of the downlink resources and the carrier frequency of the uplink resources is indicated in the system information transmitted on the downlink resources.
Similar assumptions for the component carrier structure apply to later releases too.
Carrier Aggregation in LTE-A for Support of Wider Bandwidth
The frequency spectrum for IMT-Advanced was decided at the World Radio communication Conference 2007 (WRC-07). Although the overall frequency spectrum for IMT-Advanced was decided, the actual available frequency bandwidth is different according to each region or country. Following the decision on the available frequency spectrum outline, however, standardization of a radio interface started in the 3rd Generation Partnership Project (3GPP). At the 3GPP TSG RAN #39 meeting, the Study Item description on “Further Advancements for E-UTRA (LTE-Advanced)” was approved. The study item covers technology components to be considered for the evolution of E-UTRA, e.g., to fulfill the requirements on IMT-Advanced.
The bandwidth that the LTE-Advanced system is able to support is 100 MHz, while an LTE system can only support 20 MHz. Nowadays, the lack of radio spectrum has become a bottleneck of the development of wireless networks, and as a result it is difficult to find a spectrum band which is wide enough for the LTE-Advanced system. Consequently, it is urgent to find a way to gain a wider radio spectrum band, wherein a possible answer is the carrier aggregation functionality.
In carrier aggregation, two or more component carriers are aggregated in order to support wider transmission bandwidths up to 100 MHz. Several cells in the LTE system are aggregated into one wider channel in the LTE-Advanced system which is wide enough for 100 MHz even though these cells in LTE may be in different frequency bands.
All component carriers can be configured to be LTE Rel. 8/9 compatible, at least when the bandwidth of a component carrier does not exceed the supported bandwidth of a LTE Rel. 8/9 cell. Not all component carriers aggregated by a user equipment may necessarily be Rel. 8/9 compatible. Existing mechanism (e.g., barring) may be used to avoid Rel-8/9 user equipments to camp on a component carrier.
A user equipment may simultaneously receive or transmit one or multiple component carriers (corresponding to multiple serving cells) depending on its capabilities. A LTE-A Rel. 10 user equipment with reception and/or transmission capabilities for carrier aggregation can simultaneously receive and/or transmit on multiple serving cells, whereas an LTE Rel. 8/9 user equipment can receive and transmit on a single serving cell only, provided that the structure of the component carrier follows the Rel. 8/9 specifications.
Carrier aggregation is supported for both contiguous and non-contiguous component carriers with each component carrier limited to a maximum of 110 Resource Blocks in the frequency domain using the 3GPP LTE (Release 8/9) numerology.
It is possible to configure a 3GPP LTE-A (Release 10) compatible user equipment to aggregate a different number of component carriers originating from the same eNodeB (base station) and of possibly different bandwidths in the uplink and the downlink. The number of downlink component carriers that can be configured depends on the downlink aggregation capability of the UE. Conversely, the number of uplink component carriers that can be configured depends on the uplink aggregation capability of the UE. It may currently not be possible to configure a mobile terminal with more uplink component carriers than downlink component carriers.
In a typical TDD deployment, the number of component carriers and the bandwidth of each component carrier in uplink and downlink is the same. Component carriers originating from the same eNodeB need not provide the same coverage.
The spacing between centre frequencies of contiguously aggregated component carriers shall be a multiple of 300 kHz. This is in order to be compatible with the 100 kHz frequency raster of 3GPP LTE (Release 8/9) and at the same time preserve orthogonality of the subcarriers with 15 kHz spacing. Depending on the aggregation scenario, the n*300 kHz spacing can be facilitated by insertion of a low number of unused subcarriers between contiguous component carriers.
The nature of the aggregation of multiple carriers is only exposed up to the MAC layer. For both uplink and downlink there is one HARQ entity required in MAC for each aggregated component carrier. There is (in the absence of SU-MIMO for uplink) at most one transport block per component carrier. A transport block and its potential HARQ retransmissions need to be mapped on the same component carrier.
The Layer 2 structure with activated carrier aggregation is shown in FIG. 5 and FIG. 6 for the downlink and uplink respectively.
When carrier aggregation is configured, the mobile terminal only has one RRC connection with the network. At RRC connection establishment/re-establishment, one cell provides the security input (one ECGI, one PCI and one ARFCN) and the non-access stratum mobility information (e.g., TAI) similarly as in LTE Rel. 8/9. After RRC connection establishment/re-establishment, the component carrier corresponding to that cell is referred to as the downlink Primary Cell (PCell). There is always one and only one downlink PCell (DL PCell) and one uplink PCell (UL PCell) configured per user equipment in connected state. Within the configured set of component carriers, other cells are referred to as Secondary Cells (SCells); with carriers of the SCell being the Downlink Secondary Component Carrier (DL SCC) and Uplink Secondary Component Carrier (UL SCC).
The configuration and reconfiguration, as well as addition and removal, of component carriers can be performed by RRC. Activation and deactivation is done via MAC control elements. At intra-LTE handover, RRC can also add, remove, or reconfigure SCells for usage in the target cell. When adding a new SCell, dedicated RRC signaling is used for sending the system information of the SCell, the information being necessary for transmission/reception (similarly as in Rel-8/9 for handover).
When a user equipment is configured with carrier aggregation there is at least one pair of uplink and downlink component carriers that is always active. The downlink component carrier of that pair might be also referred to as ‘DL anchor carrier’. Same applies also for the uplink.
When carrier aggregation is configured, a user equipment may be scheduled on multiple component carriers simultaneously but at most one random access procedure shall be ongoing at any time. Cross-carrier scheduling allows the PDCCH of a component carrier to schedule resources on another component carrier. For this purpose a component carrier identification field is introduced in the respective DCI formats, called CIF.
A linking, established by RRC signaling, between uplink and downlink component carriers allows identifying the uplink component carrier for which the grant applies when there is no-cross-carrier scheduling. The linkage of downlink component carriers to uplink component carrier does not necessarily need to be one to one. In other words, more than one downlink component carrier can link to the same uplink component carrier. At the same time, a downlink component carrier can only link to one uplink component carrier.
Channel State Information Feedback Elements
Commonly, mobile communication systems define special control signalling that is used to convey the channel quality feedback. In 3GPP LTE, there exist three basic elements which may or may not be given as feedback for the channel quality. These channel quality elements are:                MCSI: Modulation and Coding Scheme Indicator, sometimes referred to as Channel Quality Indicator (CQI) in the LTE specification        PMI: Precoding Matrix Indicator        RI: Rank Indicator        
The MCSI suggests a modulation and coding scheme that should be used for transmission, while the PMI points to a pre-coding matrix/vector that is to be employed for spatial multiplexing and multi-antenna transmission (MIMO) using a transmission matrix rank that is given by the RI. Details about the involved reporting and transmission mechanisms are given in the following specifications to which it is referred for further reading (all documents available at http://www.3gpp.org and incorporated herein by reference):                3GPP TS 36.211, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation” (3GPP TS 36.211, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation”), version 10.0.0, particularly sections 6.3.3 and 6.3.4;        3GPP TS 36.212, “Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding” (3GPP TS 36.212, “Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding”, version 10.0.0), version 10.0.0, particularly sections 5.2.2, 5.2.4, and 5.3.3; and        3GPP TS 36.213, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures” (3GPP TS 36.213, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures”, version 10.0.1), version 10.0.1, particularly sections 7.1.7 and 7.2.        
In 3GPP LTE, not all of the above identified three channel quality elements are necessarily reported at the same time. The elements being actually reported depend mainly on the configured reporting mode. It should be noted that 3GPP LTE also supports the transmission of two codewords (i.e., two codewords of user data (transport blocks) may be multiplexed to and transmitted in a single sub-frame), so that feedback may be given either for one or two codewords. Some details are provided in the next sections and in Table 1 below for an exemplary scenario using a 20 MHz system bandwidth. It should be noted that this information is based on 3GPP TS 36.213, section 7.2.1 mentioned above.
The individual reporting modes for the aperiodic channel quality feedback are defined in 3GPP LTE as follows:
Reporting Mode 1-2
Contents of this report:
                One set S (i.e., wideband) MCSI value per codeword        One precoding matrix, represented by a PMI, for each subband        In some cases (See 3GPP TS 36.213 clause 7.2.1), additionally one set S (i.e., wideband) PMI value        In case of transmission modes 4, 8, 9, and 10: One RI valueReporting Mode 2-0Contents of this report:        One set S (i.e., wideband) MCSI value        Positions of M selected subbands        One MCSI value for the M selected subbands (2 bits differential to the set S MCSI value, non-negative)        In case of transmission mode 3: One RI valueReporting Mode 2-2Contents of this report:        One set S (i.e., wideband) MCSI value per codeword        One preferred PMI for set S (i.e., wideband)        Positions of M selected subbands        One MCSI value for the M selected subbands per codeword (2 bits differential to the corresponding set S MCSI value, non-negative)        One preferred PMI for M selected subbands—In some cases (See 3GPP TS 36.213 clause 7.2.1), additionally one set S (i.e., wideband) PMI value        In case of transmission modes 4, 8, 9, and 10: One RI valueReporting Mode 3-0Contents of this report:        One set S (i.e., wideband) MCSI value        One MCSI value per subband (2 bits differential to set S MCSI value)        In case of transmission mode 3: One RI valueReporting Mode 3-1Contents of this report:        One set S (i.e., wideband) MCSI value per codeword        One preferred PMI for set S (i.e., wideband)                    In some cases (See 3GPP TS 36.213 clause 7.2.1), additionally one set S (i.e., wideband) PMI value                        One MCSI value per codeword per subband (2 bits differential to them corresponding set S MCSI value)        In case of transmission modes 4, 8, 9, and 10: One RI valueReporting Mode 3-2Contents of this report:        One set S (i.e., wideband) MCSI value per codeword        One precoding matrix, represented by a PMI, for each subband—In some cases (See 3GPP TS 36.213 clause 7.2.1), additionally one set S (i.e., wideband) PMI value        One MCSI value per codeword per subband (2 bits differential to the corresponding set S MCSI value)        In case of transmission modes 4, 8, 9, and 10: One RI value        
It should be noted that the term subband is here used so as to represent a number of resource blocks as outlined earlier, while the term set S represents generally a subset of the whole set of resource blocks in the system bandwidth. In the context of 3GPP LTE and LTE-A, the set S so far is defined to always represent the whole cell, i.e., component carrier bandwidth, a frequency range of up to 20 MHz, and is for simplicity hereafter referred to as “wideband”.
Aperiodic & Periodic CQI Reporting
The periodicity and frequency resolution to be used by a UE to report the CSI are both controlled by the eNodeB. The Physical Uplink Control Channel (PUCCH) is used for periodic CSI reporting only; the PUSCH is used for aperiodic reporting of the CSI, whereby the eNodeB specifically instructs the UE to send an individual CSI report embedded into a resource which is scheduled for uplink data transmission.
In order to acquire CSI information quickly, eNodeB can schedule aperiodic CSI by setting a CSI request bit in an uplink resource grant sent on the Physical Downlink Control Channel.
In 3GPP LTE, a simple mechanism is foreseen to trigger the so-called aperiodic channel quality feedback from the user equipment. An eNodeB in the radio access network sends an L1/L2 control signal to the user equipment to request the transmission of the so-called aperiodic CSI report (see 3GPP TS 36.212, section 5.3.3.1.1 and 3GPP TS 36.213, section 7.2.1 for details). Another possibility to trigger the provision of aperiodic channel quality feedback by the user equipments is linked to the random access procedure (see 3GPP TS 36.213, section 6.2).
Whenever a trigger for providing channel quality feedback is received by the user equipment, the user equipment subsequently transmits the channel quality feedback to the eNodeB. Commonly, the channel quality feedback (i.e., the CSI report) is multiplexed with uplink (user) data on the Physical Uplink Shared CHannel (PUSCH) resources that have been assigned to the user equipment by the L1/L2 signal (such as the PDCCH) which triggered the channel quality feedback.
Downlink Reference Signals
In the LTE downlink, five different types of RSs are provided:                Cell-specific RSs (often referred to as ‘common’ RSs, as they are available to all UEs in a cell and no UE-specific processing is applied to them);        UE-specific RSs (introduced in Release 8 and extended in release 9 and 10), which may be embedded in the data for specific UEs (also known as Demodulation Reference Signals—DM-RSs).        MBSFN-specific RSs, which are used only for Multimedia Broadcast Single Frequency Network (MBSFN) operation.        Positioning RSs, which from Release 9 onwards may be embedded in certain ‘positioning subframes’ for the purpose of UE location measurements.        Channel State Information, CSI, RSs, which are introduced in release 10 specifically for the purpose of estimating the downlink channel state and not for data demodulation.        
Each RS pattern is transmitted from an antenna port at the eNodeB. An antenna port may in practice be implemented either as a single physical transmit antenna, or as a combination of multiple physical antenna elements. In either case, the signal transmitted from each antenna port is not designed to be further deconstructed by the UE receiver:
The transmitted RS corresponding to a given antenna port defines the antenna port from the point of view of the UE, and enables the UE to derive a channel estimate for all data transmitted on that antenna port—regardless of whether it represents a single radio channel from one physical antenna or a composited channel from a plurality of physical antenna elements together comprising the antenna port.
Cell-Specific Reference Signals
The cell specific RSs enable the UE to determine the phase reference for demodulating the downlink control channels and the downlink data in most transmission modes of the Physical Downlink Share Channel, PDSCH. If UE-specific pre-coding is applied to the PDSCH data symbols before transmission downlink control signaling is provided to inform the UE of the corresponding phase adjustment is should apply relative to the phase reference provided by the cell-specific reference signals.
In an OFDM-based system an equidistant arrangement of reference symbols in the lattice structure achieves the Minimum Mean-Squared Error (MMSE) estimate of the channel. Moreover, in the case of a uniform reference symbol grid, a ‘diamonds shape’ in the time-frequency plane can be shown to be optimal.
In LTE, the arrangement of REs on which the cell-specific RSs are transmitted follows these principles. FIG. 7 illustrates the RS arrangement where the cell-specific reference signals are indicated with P, namely, as {P0, P1, P2, P3}.
Up to four cell-specific antenna ports, numbered 0-3, may be used in LTE eNodeB, thus requiring the UE to derive up to four separate channel estimates. For each antenna port, a different RS pattern has been designed, with particular attention having been given to the minimization of intra-cell interference between the multiple transmit antenna ports.
In FIG. 7, Px indicates that the RE is used for the transmission of an RS on antenna port X. Then an RE is used to transmit an RS on one antenna port, the corresponding RE on the other antenna ports is set to zero to limit the interference.
Downlink Reference Signals for Estimation of Channel State Information (CSI-RS)
The main goal of CSI-RS is to obtain channel state feedback for up to eight transmit antenna ports to assist the eNodeB in its precoding operation. LTE release 10 supports transmission of CSI-RS for 1, 2, 4, and 8 transmit antenna ports. CSI-RS also enables the UE to estimate the CSI for multiple cells rather than just one serving cell, to support future multi-cell cooperative transmission schemes.
The following general design principles can be identified for CSI-RS:                In the frequency domain, uniform spacing of CSI-RS location is highly desirable:        In the time domain, it is desirable to minimize the number of subframes containing CSI-RS, so that a UE can estimate the CSI for different antenna ports and even different cells with minimum wake-up duty calycle when the UE is in Discontinuous Reception (DRX) mode, to preserve battery life.        The overall CSI-RS overhead involves a trade-off between accuracy CSI estimation for efficient operation and minimizing the impact on legacy pre-Release 10 UEs which are unaware of the presence of CSI-RS and whose data are punctured by the CSI-RS transmission.        CSI-RS of different antenna ports within a cell, and, as far as possible, form different cells, should be orthogonally multiplexed to enable accuracy CSI estimation.        
Taking these considerations into account, the CSI-RS patterns selected for Release 10 are shown in FIG. 7. CDM codes of length 2 are used so the CSI-RS on two antenna ports share two REs on a given subcarrier.
The pattern shown in FIG. 7 can be used in both frame structure 1 (Frequency Division Duplex, FDD), and frame structure 2 (Time Division Duplex, TDD). The REs used for CSI-RSs are labeled RS and used together with the following table grouping the CSI-RS into CSI reference signal configuration.
In addition the following table includes for each CSI reference signal configuration an identification of the cell index as one of the set of {A, B, C, D, E, F, G, H, I, J, K, L, V, N, O, P, Q, R, S, T} or a subset thereof and the antenna port and the maximum 8 antenna ports grouped into CDM groups {x, z, u}.
TABLE 1Number of CSI reference signals configured1 or 24BCSI CellCellCellreferenceindex,index,index,signalCDMCDMCDMconfiguration(k′, l′)n, mod 2group(k′, l′)n, mod 2group(k′, l′)n, mod 2groupFrame 0(9.5)0Ax(9.5)0Ax(9.5)0Axstructure1(11.2)1Bx(11.2)1Bx(11.2)1Bxtype 12(9.2)1Cx(9.2)1Cx(9.2)1Cxand 23(7.2)1Dx(7.2)1Dx(7.2)1Dx4(9.5)1Ex(9.5)1Ex(9.5)1Ex5(8.5)0Fx(8.5)0Fx(Az)6(10.2)1Gx(10.2)1Gx(Bz)7(8.2)1Hx(8.2)1Hx(Cz)8(6.2)1Ix(6.2)1Ix(Dz)9(8.5)1Jx(8.5)1Jx(Ez)10(3.5)0Kx(Ay)(Ay)11(2.5)0Lx(Fy)(Au)12(5.2)1Vx(By)(By)13(4.2)1Nx(Gy)(Bu)14(3.2)1Ox(Cy)(Cy)15(2.2)1Px(Hy)(Cu)16(1.2)1Qx(Dy)(Dy)17(0.2)1Rx(Iy)(Du)18(3.5)1Sx(Ey)(Ey)19(2.5)1Tx(Jy)(Eu)Frame20(11.1)1Ax(11.1)1Ax(11.1)1Axstructure21(9.1)1Bx(9.1)1Bx(9.1)1Bxtype 222(7.1)1Cx(7.1)1Cx(7.1)1Cxonly23(10.1)1Dx(10.1)1Dx(Az)24(8.1)1Ex(8.1)1Ex(Bz)25(6.1)1Fx(6.1)1Fx(Cz)26(5.1)1Gx(Ay)(Ay)27(4.1)1Hx(Dy)(Au)28(3.1)1Ix(By)(By)29(2.1)1Jx(Ey)(Bu)30(1.1)1Kx(Cy)(Cy)31(0.1)1Lx(Fy)(Cu)
The table corresponds to that included 3GPP TS 36.211 V12.3.0 under section 6.10.5.2 in Table 6.10.5.2-1: illustrating a mapping from CSI reference signal configuration to (k′, l′) for normal cyclic prefix, additionally including the identification of Cell index, CDM group.
In addition, Cell index and CDM group entries in brackets are meant to indicate which index/group combination corresponds to which RE location (k′, l′) within the time/frequency grids of a resource block; but it is not intended to indicate that a corresponding CSI reference signal configuration index is supported, rather the dependency follows implicitly from other parts of 3GPP TS 36.211 V12.3.0. Consequently, those entries in brackets should be understood just for illustrational purposes.
Layer 1/Layer 2 (L1/L2) Control Signaling
In order to inform the scheduled users about their allocation status, transport format and other transmission-related information (e.g., HARQ information, transmit power control (TPC) commands), L1/L2 control signaling is transmitted on the downlink along with the data. L1/L2 control signaling is multiplexed with the downlink data in a subframe, assuming that the user allocation can change from subframe to subframe.
It should be noted that user allocation might also be performed on a TTI (Transmission Time Interval) basis, where the TTI length can be a multiple of the subframes. The TTI length may be fixed in a service area for all users, may be different for different users, or may even be dynamic for each user. Generally, the L1/2 control signaling need only be transmitted once per TTI. Without loss of generality, the following assumes that a TTI is equivalent to one subframe.
The L1/L2 control signaling is transmitted on the Physical Downlink Control Channel (PDCCH). A PDCCH carries a message as Downlink Control Information (DCI), which in most cases includes resource assignments and other control information for a mobile terminal or groups of UEs. In general, several PDCCHs can be transmitted in one subframe.
It should be noted that in 3GPP LTE, assignments for uplink data transmissions, also referred to as uplink scheduling grants or uplink resource assignments, are also transmitted on the PDCCH. Furthermore, Release 11 introduced an EPDCCH that fulfills basically the same function as the PDCCH, i.e., conveys L1/L2 control signaling, even though the detailed transmission methods are different from the PDCCH.
Further details can be found particularly in the current versions of 3GPP TS 36.211 and 36.213, incorporated herein by reference. Consequently, most items outlined in the background and the embodiments apply to PDCCH as well as EPDCCH, or other means of conveying L1/L2 control signals, unless specifically noted.
Generally, the information sent on the L1/L2 control signaling for assigning uplink or downlink radio resources (particularly LTE(-A) Release 10) can be categorized to the following items:                User identity, indicating the user that is allocated. This is typically included in the checksum by masking the CRC with the user identity;        Resource allocation information, indicating the resources (Resource Blocks, RBs) on which a user is allocated. Alternatively this information is termed resource block assignment (RBA). Note that the number of RBs on which a user is allocated can be dynamic;        Carrier indicator, which is used if a control channel transmitted on a first carrier assigns resources that concern a second carrier, i.e., resources on a second carrier or resources related to a second carrier; (cross carrier scheduling);        Modulation and coding scheme that determines the employed modulation scheme and coding rate;        HARQ information, such as a new data indicator (NDI) and/or a redundancy version (RV) that is particularly useful in retransmissions of data packets or parts thereof;        Power control commands to adjust the transmit power of the assigned uplink data or control information transmission;        Reference signal information such as the applied cyclic shift and/or orthogonal cover code index, which are to be employed for transmission or reception of reference signals related to the assignment;        Uplink or downlink assignment index that is used to identify an order of assignments, which is particularly useful in TDD systems;        Hopping information, e.g., an indication whether and how to apply resource hopping in order to increase the frequency diversity;        CSI request, which is used to trigger the transmission of channel state information in an assigned resource; and        Multi-cluster information, which is a flag used to indicate and control whether the transmission occurs in a single cluster (contiguous set of RBs) or in multiple clusters (at least two non-contiguous sets of contiguous RBs). Multi-cluster allocation has been introduced by 3GPP LTE-(A) Release 10.        
It is to be noted that the above listing is non-exhaustive, and not all mentioned information items need to be present in each PDCCH transmission depending on the DCI format that is used.
Downlink control information occurs in several formats that differ in overall size and also in the information contained in their fields. The different DCI formats that are currently defined for LTE are as follows and described in detail in 3GPP TS 36.212, “Multiplexing and channel coding”, section 5.3.3.1 (current version v12.2.0 available at http://www.3gpp.org and incorporated herein by reference). In addition, for further information regarding the DCI formats and the particular information that is transmitted in the DCI, please refer to the mentioned technical standard or to LTE—The UMTS Long Term Evolution—From Theory to Practice, Edited by Stefanie Sesia, Issam Toufik, Matthew Baker, Chapter 9.3, incorporated herein by reference.
Format 0: DCI Format 0 is used for the transmission of resource grants for the PUSCH, using single-antenna port transmissions in uplink transmission mode 1 or 2.
Format 1: DCI Format 1 is used for the transmission of resource assignments for single codeword PDSCH transmissions (downlink transmission modes 1, 2, and 7). Format 1A: DCI Format 1A is used for compact signaling of resource assignments for single codeword PDSCH transmissions, and for allocating a dedicated preamble signature to a mobile terminal for contention-free random access (for all transmissions modes).Format 1B: DCI Format 1B is used for compact signaling of resource assignments for PDSCH transmissions using closed loop precoding with rank-1 transmission (downlink transmission mode 6). The information transmitted is the same as in Format 1A, but with the addition of an indicator of the precoding vector applied for the PDSCH transmission.Format 1C: DCI Format 1C is used for very compact transmission of PDSCH assignments. When format 1C is used, the PDSCH transmission is constrained to using QPSK modulation. This is used, for example, for signaling paging messages and broadcast system information messages.Format 1D: DCI Format 1D is used for compact signaling of resource assignments for PDSCH transmission using multi-user MIMO. The information transmitted is the same as in Format 1B, but instead of one of the bits of the precoding vector indicators, there is a single bit to indicate whether a power offset is applied to the data symbols. This feature is needed to show whether or not the transmission power is shared between two UEs. Future versions of LTE may extend this to the case of power sharing between larger numbers of UEs.Format 2: DCI Format 2 is used for the transmission of resource assignments for PDSCH for closed-loop MIMO operation (transmission mode 4).Format 2A: DCI Format 2A is used for the transmission of resource assignments for PDSCH for open-loop MIMO operation. The information transmitted is the same as for Format 2, except that if the eNodeB has two transmit antenna ports, there is no precoding information, and for four antenna ports two bits are used to indicate the transmission rank (transmission mode 3).Format 2B: Introduced in Release 9 and is used for the transmission of resource assignments for PDSCH for dual-layer beamforming (transmission mode 8).Format 2C: Introduced in Release 10 and is used for the transmission of resource assignments for PDSCH for closed-loop single-user or multi-user MIMO operation with up to 8 layers (transmission mode 9).Format 2D: introduced in Release 11 and used for up to 8 layer transmissions; mainly used for COMP (Cooperative Multipoint) (transmission mode 10)Formats 3 and 3A: DCI formats 3 and 3A are used for the transmission of power control commands for PUCCH and PUSCH with 2-bit or 1-bit power adjustments, respectively. These DCI formats contain individual power control commands for a group of UEs.Format 4: DCI format 4 is used for the scheduling of the PUSCH, using closed-loop spatial multiplexing transmissions in uplink transmission mode 2.Transmission Modes for the PDSCH (Physical Downlink Shared Channel)
The Physical Downlink Shared CHannel (PDSCH) is the main data bearing downlink channel in LTE. It is used for all user data, as well as for broadcast system information which is not carried on the PBCH, and for paging messages—there is no specific physical layer paging channel in LTE. Data is transmitted on the PDSCH in units known as Transport Blocks (TBs), each of which corresponds to a Medium Access Control (MAC) layer protocol data unit (PDU). Transport blocks may be passed down from the MAC layer to the physical layer once per Transmission Time Interval (TTI), where a TTI is one ms, corresponding to the subframe duration.
When employed for user data, one or, at most, two transport blocks can be transmitted per UE per subframe per component carrier, depending on the transmission mode selected for the PDSCH for each UE. In LTE, usually there are multiple antennas for downlink, i.e., the eNodeB may use multiple transmit antennas, and the UE may use multiple receiving antennas. The two antennas can be used in diverse configurations, which are distinguished and denoted as transmission modes in LTE. The UE is configured by the eNodeB with a particular transmission mode. For instance, the single transmission antenna in single receiver antenna mode is called transmission mode 1.
The various transmission modes are defined in the 3GPP technical standard TS 36.213 (current version 12.3.0), subclause 8.0 for the uplink (particularly Tables 8-3, 8-3A, 8-5, and 8-5A) and subclause 7.1 for the downlink (particularly Tables 7.1-1, 7.1-2, 7.1-3, 7.1-5, 7.1-5A, 7.1-6, 7.1-6A, and 7.1-7); these are incorporated herein by reference. These tables from 3GPP TS 36.213 show the relationship between RNTI Type (e.g., C-RNTI, SPS C-RNTI, SI-RNTI), the Transmission Mode and the DCI format.
These tables provide several predefined transmission modes identifying the particular transmission scheme to be used for the PDSCH corresponding to the (E)PDCCH.
LTE on Unlicensed Bands—Licensed-Assisted Access LAA
In September 2014, 3GPP initiated a new study item on LTE operation on unlicensed spectrum. The reason for extending LTE to unlicensed bands is the ever-growing demand for wireless broadband data in conjunction with the limited amount of licensed bands. Unlicensed spectrum therefore is more and more considered by cellular operators as a complementary tool to augment their service offering. The advantage of LTE in unlicensed bands compared to relying on other radio access technologies (RAT) such as Wi-Fi is that complementing the LTE platform with unlicensed spectrum access enables operators and vendors to leverage the existing or planned investments in LTE/EPC hardware in the radio and core network.
However, it has to be taken into account that unlicensed spectrum access can never match the qualities of licensed spectrum due to the inevitable coexistence with other radio access technologies (RATs) in the unlicensed spectrum. LTE operation on unlicensed bands will therefore at least in the beginning be considered rather a complement to LTE on licensed spectrum than stand-alone operation on unlicensed spectrum. Based on this assumption, 3GPP established the term Licensed Assisted Access (LAA) for the LTE operation on unlicensed bands in conjunction with at least one licensed band. Future stand-alone operation of LTE on unlicensed spectrum without relying on LAA however shall not be excluded.
The current intended general LAA approach at 3GPP is to make use of the already specified Rel-12 carrier aggregation (CA) framework as much as possible where the CA framework configuration comprises a so-called primary cell (PCell) carrier and one or more secondary cell (SCell) carriers. CA supports in general both self-scheduling of cells (scheduling information and user data are transmitted on the same component carrier) and cross-carrier scheduling between cells (scheduling information in terms of PDCCH/EPDCCH and user data in terms of PDSCH/PUSCH are transmitted on different component carriers).
A very basic scenario is illustrated in FIG. 8, with a licensed PCell, licensed SCell 1, and various unlicensed SCells 2, 3, and 4 (exemplarily depicted as small cells). The transmission/reception network nodes of unlicensed SCells 2, 3, and 4 could be remote radio heads managed by the eNB, or could be nodes that are attached to the network but not managed by the eNB. For simplicity, the connection of these nodes to the eNB or to the network is not explicitly shown in the figure.
At present, the basic approach envisioned at 3GPP is that the PCell will be operated on a licensed band while one or more SCells will be operated on unlicensed bands. The benefit of this strategy is that the PCell can be used for reliable transmission of control messages and user data with high quality of service (QoS) demands, such as, for example, voice and video, while a PCell on unlicensed spectrum might yield, depending on the scenario, to some extent significant QoS reduction due to inevitable coexistence with other RATs.
It has been agreed during RAN1#78bis, that the LAA investigation at 3GPP will focus on unlicensed bands at 5 GHz, although no final decision is taken. One of the most critical issues is therefore the coexistence with Wi-Fi (IEEE 802.11) systems operating at these unlicensed bands. In order to support fair coexistence between LTE and other technologies such as Wi-Fi as well as fairness between different LTE operators in the same unlicensed band, the channel access of LTE for unlicensed bands has to abide by certain sets of regulatory rules which depend on region and considered frequency band.
A comprehensive description of the regulatory requirements for operation on unlicensed bands at 5 GHz is given in R1-144348, “Regulatory Requirements for Unlicensed Spectrum” (R1-144348, “Regulatory Requirements for Unlicensed Spectrum”), Alcatel-Lucent et al., RAN1#78bis, September 2014, incorporated herein by reference. Depending on region and band, regulatory requirements that have to be taken into account when designing LAA procedures comprise Dynamic Frequency Selection (DFS), Transmit Power Control (TPC), Listen Before Talk (LBT) and discontinuous transmission with limited maximum transmission duration. The intention of the 3GPP is to target a single global framework for LAA which basically means that all requirements for different regions and bands at 5 GHz have to be taken into account for the system design.
DFS is required for certain regions and bands in order to detect interference from radar systems and to avoid co-channel operation with these systems. The intention is furthermore to achieve a near-uniform loading of the spectrum. The DFS operation and corresponding requirements are associated with a master-slave principle. The master shall detect radar interference, can however rely on another device, that is associated with the master, to implement the radar detection.
The operation on unlicensed bands at 5 GHz is in most regions limited to rather low transmit power levels compared to the operation on licensed bands resulting in small coverage areas. Even if the licensed and unlicensed carriers were to be transmitted with identical power, usually the unlicensed carrier in the 5 GHz band would be expected to support a smaller coverage area than a licensed cell in the 2 GHz band due to increased path loss and shadowing effects for the signal. A further requirement for certain regions and bands is the use of TPC in order to reduce the average level of interference caused to other devices operating on the same unlicensed band.
Following the European regulation regarding LBT, devices have to perform a Clear Channel Assessment (CCA) before occupying the radio channel. It is only allowed to initiate a transmission on the unlicensed channel after detecting the channel as free based on energy detection. The equipment has to observe the channel for a certain minimum during the CCA. The channel is considered occupied if the detected energy level exceeds a configured CCA threshold. If the channel is classified as free, the equipment is allowed to transmit immediately. The maximum transmit duration is thereby restricted in order to facilitate fair resource sharing with other devices operating on the same band.
Considering the different regulatory requirements, it is apparent that the LTE specification for operation on unlicensed bands will require several changes compared to the current Rel-12 specification that is limited to licensed band operation.
In connection with the new work item Licensed-Assisted Access it is also not finally decided how the mobile station is reporting channel state information, CSI to a base station, particularly in a scenario in which a plurality of, namely, unlicensed and licensed, component carriers are configured for communication between the mobile station and the base station for at least one of downlink and uplink transmissions. A reliable and efficient CSI reporting mechanism should be implemented taking into account the special circumstances of unlicensed carriers.